The present invention relates to an improved method for the manufacture of clevidipine (butyroxymethyl methyl 4-(2xe2x80x2,3xe2x80x2-dichlorophenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate) via the route of reacting 4-(2xe2x80x2,3xe2x80x2-dichlorophenyl)-1,4-dihydro-5-methoxycarbonyl-2,6-dimethyl-3-pyridinecarboxylic acid with chloromethyl butyrate.
WO 95/12578 discloses a method for the preparation of clevidipine using as reactants 4-(2xe2x80x2,3xe2x80x2-dichlorophenyl)-1,4-dihydro-5-methoxycarbonyl-2,6-dimethyl-3-pyridinecarboxylic acid. The disclosed method has several drawbacks.
It has now been found that clevidipine, which is a short-acting calcium-channel blocker, can be prepared in a manner that is faster, reduces the amount of byproducts, is more environmentally sound and gives a better yield than the process disclosed in WO 95/12578. It also increases the stability of one of the intermediates allowing it to be isolated and stored without drying.
The method according to the invention uses an inorganic salt instead of the neutral form of carboxylic acid.
The method which is schematically outlined below is characterized by reaction of compound A, wherein A+ is a positively charged inorganic ion with chloromethyl butyrate to obtain clevidipine. 
Compound A is reacted with chloromethyl butyrate optionally in the presence of a corresponding hydrogen carbonate (preferable KHCO3) in refluxing acetonitrile. A+ is preferably potassium or sodium, most preferably potassium. Preferably the inorganic salts are removed by filtration and the product is crystallized. The crystallization can be performed for instance by the addition of isopropanol and water with subsequent cooling. It can also be crystallized by exchanging solvent from acetonitrile to a mixture of alcohol, such as ethanol or isopropanol, preferably ethanol, and water with repeated evaporations. In the further purification of the product the crystals are washed with a mixture of water and ethanol or isopropanol. The product can be dissolved in refluxing isopropanol, crystallized by cooling, isolated by filtration and finally washed with a water and isopropanol mixture.
In a preferred embodiment Compound A is reacted with chloromethyl butyrate (1.2-2.8 eq., preferably 1.4-1.6 eq.). The reactants are charged together with potassium hydrogen carbonate (1.5-0.4 eq., preferable 0.8-0.6 eq.) and the solvent acetonitrile (3-12 ml/g of Compound A).
Preparation of Compound A starting material 
Cyanoethyl methyl 4-(2xe2x80x2,3xe2x80x2-dichlorophenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate is reacted with potassium hydroxide or other suitable hydroxide e.g. sodium hydroxide in isopropanol over night at room temperature. Some of the solvent can be evaporated off to increase the yield or the product is isolated direct without any evaporation and washed with isopropanol.